Methods and systems for reducing the level of one or more impurities that are present in a pretreated cellulosic material and/or distillate

ABSTRACT

The present invention relates to methods and systems for remediating one or more impurities (e.g., diacetyl) that are present in manufacturing an alcohol (e.g., ethanol) from cellulosic biomass. The methods and systems include reacting the one or more impurities with at least one treatment compound (e.g., an oxidizing agent, an alkali compound, or a mixture thereof) to form a reaction product that can be separated from the alcohol.

RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 14/993,285, filed Jan. 12, 2016, which is a divisionalapplication of nonprovisional patent Ser. No. 13/917,169, filed Jun. 13,2013, now U.S. Pat. No. 9,278,379, which claims priority to U.S.Provisional Application No. 61/660,043, filed Jun. 15, 2012, whichapplications are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates methods and systems for remediating one ormore impurities (e.g., diacetyl) that are present in manufacturing analcohol (e.g., ethanol) from cellulosic biomass. The methods and systemsinclude reacting the one or more impurities with at least one treatmentcompound (e.g., an oxidizing agent, an alkali compound, or a mixturethereof) to form a reaction product that can be separated from thealcohol.

BACKGROUND

Alcohol (e.g., ethanol and/or butanol) and other fermentation productsmay be produced from grain-based feedstocks (e.g. corn, sorghum/milo,barley, wheat, soybeans, etc.), from sugar (e.g. from sugar cane, sugarbeets, etc.), and from biomass (e.g. from cellulosic feedstocks such asswitchgrass, corn cobs and stover, wood or other plant material).

In a biorefinery configured to produce ethanol from biomass such ascellulosic feedstocks as indicated above, ethanol can be produced fromlignocellulosic material (e.g. cellulose and/or hemi-cellulose). Thebiomass is typically prepared so that sugars in the cellulosic material(such as glucose from the cellulose and xylose from the hemi-cellulose)can be accessed and fermented into a fermentation product that includesethanol (among other things). The fermentation product can then betransferred to a distillation system, where the ethanol can be recoveredby distillation and dehydration. Other bioproducts such as lignin andorganic acids may also be recovered as co-products.

In addition to generating ethanol (or other desired fermentationproduct) a number of ancillary chemicals may also be produced during oneor more of biomass pretreatment, saccharification, fermentation, or evendistillation. Such chemicals include substances such as acetic acid,furfural (furan-2-carbaldehyde), and diacetyl (2,3-butanedione). Some ofthese compounds may be recovered or recycled, but other compoundsrequire management or remediation in order for the cellulosicbiorefinery to operate effectively. In particular, the presence ofdiacetyl may be particularly problematic as it concentrates along withethanol during distillation and molecular sieving. Not only can diacetylcause green coloring of the ethanol to an undue degree (thereby limitingthe ethanol's downstream uses), diacetyl can also cause the ethanol tobecome more acidic over time. For fuel ethanol these are typicallyundesirable traits and can make remediation of the diacetyl desirable.

One common technique for managing undue amounts of diacetyl incellulosic ethanol includes aging the ethanol so that the diacetylbreaks down naturally. Another common technique includes blending theethanol/diacetyl mixture with a much larger volume of starch derivedethanol so as to dilute the diacetyl, thereby decreasing theconcentration of diacetyl.

Unfortunately, as cellulosic ethanol becomes more prevalent, the volumescan reach levels such that storage for long periods to “age” thediacetyl can be uneconomical, and blending may become difficult due tothe vast amounts of starch based ethanol required.

It would be advantageous to provide for systems and methods forcellulosic fermentation product treatment that can rapidly andeconomically remediate diacetyl. It would further be advantageous toprovide for systems and methods for such treatment that integrates intothe functionality of a commercial scale ethanol production facility.

SUMMARY OF THE INVENTION

The present invention relates to systems and methods for treatingcellulosic fermentation products and/or related distillate compositionsin order to reduce one or more undesirable compounds such as diacetyl toa desirable level. The present invention involves contacting acomposition that includes ethanol and diacetyl (e.g., a distillate,fermentation product, and the like) with at least one treatment compoundso that the at least one treatment compound reacts with the diacetyl toform a reaction product thereby reducing the concentration of thediacetyl. Preferably, at least a portion of the reaction product canthen be separated from the ethanol.

Advantageously, systems and methods according to the present inventioncan reduce the concentration of, e.g., diacetyl to a level so thatdiacetyl does not impact the color and/or pH of the final ethanolproduct to an undue degree. In addition, systems and methods accordingto the present invention can reduce the concentration of diacetyl inethanol in a cost effective and rapid manner.

According to one aspect of the present invention, a method of reducingthe concentration of diacetyl that is present in a pretreated cellulosicmaterial includes: providing a pretreated cellulosic material thatincludes at least one monosaccharide and diacetyl; and contacting thepretreated cellulosic material with at least one treatment compound sothat the at least one treatment compound reacts with the diacetyl toform a reaction product thereby reducing the concentration of thediacetyl. The at least one treatment compound is chosen from anoxidizing agent, an alkali compound, and mixtures thereof.

According to another aspect of the present invention, a method ofreducing the concentration of diacetyl that is present in a distillateincludes providing a pretreated cellulosic material; subjecting thepretreated cellulosic material to a fermentation process to form afermentation product that includes an alcohol and diacetyl; distillingthe fermentation product to form a distillate that includes the alcoholand the diacetyl; and contacting the distillate with at least onetreatment compound so that the at least one treatment compound reactswith the diacetyl to form a reaction product thereby reducing theconcentration of the diacetyl and forming a treated distillate, whereinthe at least one treatment compound is chosen from an oxidizing agent,an alkali compound, and mixtures thereof.

According to another aspect of the present invention, a system forreducing the concentration of diacetyl that is present in a pretreatedcellulosic material includes: a source of a fermentation product thatincludes an alcohol and diacetyl; a distillation system in fluidcommunication with the source of a fermentation product; a source of atleast one treatment compound; and a treatment system in fluidcommunication with the distillation system and the source of at leastone treatment compound. The at least one treatment compound is chosenfrom an oxidizing agent, an alkali compound, and mixtures thereof. Thedistillation system can distill the fermentation product to form adistillate that includes the alcohol and the diacetyl. The treatmentsystem causes the least one treatment compound to contact the distillateso that the at least one treatment compound reacts with the diacetyl toform a reaction product thereby reducing the concentration of thediacetyl and forming a treated distillate.

In preferred embodiments, the treatment compound includes sodiumhydroxide, hydrogen peroxide and mixtures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a biorefinery comprising an ethanolproduction facility, in accordance with some embodiments.

FIG. 1B is another perspective view of a biorefinery comprising anethanol production facility, in accordance with some embodiments.

FIG. 2 is a process flow diagram illustrating the preparation ofbiomass, in accordance with some embodiments.

FIGS. 3A to 3C are process flow diagrams illustrating examples ofethanol production processes from biomass to ethanol, in accordance withsome embodiments.

FIG. 4 is a process flow diagram illustrating the remediation treatmentprocess, in accordance with some embodiments.

FIG. 5 shows a graph of diacetyl concentration over time in peroxidetreated samples according to Example 4.

FIG. 6 shows a graph of diacetyl concentration over time in alkalitreated samples according to Example 4.

FIG. 7 shows a graph of diacetyl concentration over time in peroxide andalkali treated samples according to Example 4.

FIG. 8 shows a graph of diacetyl concentration over time in peroxidetreated samples when exposed to light or darkness in accordance withExample 5.

FIG. 9 shows a graph of diacetyl concentration over various fermentationbatches according to Example 6.

FIG. 10 shows a graph of pH of ethanol dependent upon alkali treatedsamples according to Example 6.

FIG. 11 shows a graph of pH of ethanol dependent upon alkali treatedcomposite samples according to Example 6.

FIG. 12 shows a graph of diacetyl concentration dependent upon pHaccording to Example 6.

FIG. 13 shows a graph of diacetyl concentration dependent upon pH forcomposite samples according to Example 6.

FIG. 14 shows a graph of pH of ethanol dependent upon alkali treatmentfor acetic acid buffered samples according to Example 6.

FIG. 15 shows a graph of diacetyl concentration for untreated samplesand treated distillate according to Example 6.

FIG. 16 shows a graph of acetic acid concentration of the feed,concentrate and distillate over time according to Example 6.

DETAILED DESCRIPTION

The present invention will now be further described with reference toexemplary embodiments. In the following description, numerous specificdetails are set forth in order to provide a thorough understanding ofembodiments of the present invention. It will be apparent, however, toone skilled in the art, that embodiments may be practiced without someor all of these specific details. In other instances, well known processsteps and/or structures have not been described in detail in order tofacilitate explaining the present invention. The features and advantagesof embodiments may be better understood with reference to the drawingsand discussions that follow.

The present invention relates to systems and methods to reduce theconcentration of one or more undesirable components that are generatedduring at least one of pretreating, saccharification, or fermentation ofcellulosic biomass material, or distillation of fermented cellulosicbiomass material.

Cellulosic biomass material is well-known and includes polysaccharidessuch as cellulose and/or hemicellulose. Exemplary cellulosic feedstockfor use in the present invention includes one or more of wood material,switch grass, agricultural waste, municipal waste, bagasse, etc. In someembodiments, a preferred cellulosic biomass material includes materialfrom the corn plant, such as corn cobs, corn plant husks and corn plantleaves and corn stalks (e.g. at least upper half or three-quartersportion of the stalk) (also referred to as corn stover). For example,the corn plant material may include any of (by weight) up to 100 percentcobs, up to 100 percent husks/leaves, approximately 50 percent cobs andapproximately 50 percent husks/leaves, approximately 30 percent cobs andapproximately 50 percent husks/leaves and approximately 20 percentstalks, or any of a wide variety of other combinations of cobs,husks/leaves and stalks from the corn plant. According to someembodiments, the lignocellulosic plant material of the biomass (from thecorn plant) can include (by weight) cellulose at about 30 to 55 percent,hemicellulose at about 20 to 50 percent, and lignin at about 10 to 25percent. According to alternative embodiments, the lignocellulosic plantmaterial may include fiber from the corn kernel (e.g. in somecombination with other plant material). According to one preferredembodiment, the biomass may include at least 20 to 30 percent corn cobs(by weight) with corn stover and other matter.

The cellulosic biomass material is preferably selected to convert one ormore polysaccharides such as hemicellulose or cellulose into one or moremonosaccharides such as pentose (e.g., xylose) or hexose (e.g.,glucose), which can be used to generate one or more fermentationproducts. Exemplary fermentation products include alcohol (e.g.,ethanol, butanol, and the like) due to the utility of alcohol as a fuel.However, any fermentation product resulting from the conversion ofcellulosic materials into sugars and biological conversion is consideredwithin the scope of this disclosure.

Biorefinery plant facilities for producing alcohol from biomass are wellknown. Briefly, exemplary biorefinery plant facilities are describedherein in connection with FIGS. 1A and 1B. FIG. 1A shows biorefinery 100that includes an ethanol production facility configured to produceethanol from biomass. The exemplary biorefinery 100 includes an area 102where biomass is delivered and prepared to be supplied to the ethanolproduction facility. The cellulosic ethanol production facility 100includes equipment for preparation 102, pre-treatment 104 and conversionof the biomass into material (e.g., sugars) suitable for fermentationinto one or more fermentation products in a fermentation system 106. Thecellulosic ethanol production facility 100 includes a distillationsystem 108 in which the fermentation product is distilled and dehydratedinto ethanol. As shown in FIG. 1A, a waste treatment system 110 includesan anaerobic digester and a generator. Waste treatment system 110 caninclude additional equipment configured to treat, process, and recovercomponents from the cellulosic ethanol production process, such as asolid/waste fuel boiler, anaerobic digester, or other biochemical orchemical reactors.

FIG. 1B illustrates that a biorefinery 112 may include a cellulosicethanol production facility 114 (which produces ethanol fromlignocellulosic material and components of the corn plant) co-locatedwith a corn-based ethanol production facility 116 (which producesethanol from starch contained in the endosperm component of the cornkernel). As indicated in FIG. 1B, by co-locating the two ethanolproduction facilities, certain plant systems may be shared, for example,systems for dehydration, storage, denaturing and transportation ofethanol, energy/fuel-to-energy generation systems, plant management andcontrol systems, and other systems. Corn fiber (a component of the cornkernel), which can be made available when the corn kernel is preparedfor milling (e.g. by fractionation) in the corn-based ethanol productionfacility, may be supplied to the cellulosic ethanol production facilityas a feedstock. Fuel or energy sources such as methane or lignin fromthe cellulosic ethanol production facility may be used to supply powerto either or both co-located facilities. According to other alternativeembodiments, a biorefinery (e.g. a cellulosic ethanol productionfacility) may be co-located with other types of plants and facilities,for example an electric power plant, a waste treatment facility, alumber mill, a paper plant, or a facility that processes agriculturalproducts.

FIG. 2 illustrates an exemplary system 200 for preparation of biomassdelivered to a biorefinery 100. The biomass preparation system 200 mayinclude equipment for receiving/unloading the biomass, cleaning (e.g.removal of foreign matter), grinding (e.g. milling, reduction ordensification), and transport and conveyance for processing at theplant. According to an exemplary embodiment, biomass in the form of corncobs and stover may be delivered to the biorefinery and stored 202 (e.g.in bales, piles or bins, etc.) and managed for use at the facility. Asshown, system 200 also includes preparation system 204, which isconfigured to prepare any of a wide variety of types of biomass (e.g.plant material) for treatment and processing into ethanol and otherbioproducts at the plant.

FIGS. 3A to 3C illustrate exemplary process flow diagrams 300 a, 300 band 300 c for processing biomass that has been prepared, e.g., asdescribed above with respect to FIG. 2. The process flow diagrams shownin FIGS. 3A to 3C illustrate pretreating, fermenting, distillation, andtreatment of the distillate from distillation. An example of a treatmentsystem for treating distillate to reduce the concentration of diacetylaccording to the present invention is described in more detail below inconnection with FIG. 4.

As shown in FIGS. 3A to 3C, after preparing the biomass, e.g., in system200, the biomass is mixed with water into a slurry and is pre-treatedvia a pre-treatment system 302. In the pre-treatment system 302, thebiomass can be at least partially broken down (e.g. by hydrolysis) intoone ore more oligosaccharides and/or monosaccharides (e.g., pentoses (C5sugars) and/or hexoses (C6 sugars)). Exemplary monosaccharides includexylose and glucose. Pretreatment may include the addition of one morechemicals (e.g., an acid) to promote hydrolysis of hemicelluose and/orcellulose in the biomass so as to generate one or more oligosaccharidesand/or monosaccharides. Such pretreatment of cellulosic biomass iswell-known and is disclosed in, e.g., U.S. Pat. No. 5,424,417 (Torget etal.) and U.S. Pat. No. 6,022,419 (Torget et al.), wherein the entiretiesof said documents are incorporated herein by reference for all purposes.

After pretreatment 302, as shown in FIGS. 3A-3C, separation system 304can separate a liquid fraction (e.g. a stream including C5 sugars, knownas pentose liquor) and a solids fraction (e.g. a stream includingcellulose from which the C6 sugars can be made available via solidsdisruption and/or enzymatic hydrolysis (discussed below)).

As shown in FIG. 3A, the solids in the solid stream from separationsystem 304 are disrupted via a disruption system 310 to make the solidsmore accessible to enzymes during enzymatic hydrolysis of the solids togenerate one or more C6 sugars from cellulose. Techniques for disruptingbiomass solids to increase accessibility during enzymatic hydrolysis arewell-known and include mechanical disruption, sonic disruption, and/orsteam explosion.

The C5-sugar-containing liquid component (C5 stream or pentose liquor)from separation system 304 may be returned to a joint enzyme hydrolysissystem 312 which may enzymatically generate sugars from a combinedsolids and liquids stream. Subsequently, the slurry from system 312 mayenter a fermentation system 318 so that at least one of anoligosaccharide and/or a monosaccharide in the pretreated cellulosicmaterial can be fermented to generate a fermentation product thatincludes an alcohol and diacetyl.

After fermentation in system 318, the fermentation product can bedistilled in distillation system 320 to form a distillate that includesan alcohol (e.g., ethanol) and diacetyl. The distillate may also includelignin stillage.

As shown in FIG. 3A, the ethanol from distillation system 320 can beprocessed by a treatment system 330 according to the present inventionfor remediation of one or more undesired components (e.g., reduce theconcentration of diacetyl in the ethanol).

After separation system 304 in each of FIGS. 3B and 3C, theC5-sugar-containing liquid component (C5 stream or pentose liquor) maybe treated in a pentose cleanup treatment system 306. During treatmentof the C5 and/or C6 stream, components may be processed to recoveredbyproducts, such as organic acids and lignin. The C6-sugar-containingpretreated solids component may be treated in a solids treatment system308 using enzyme hydrolysis to generate sugars. In some embodiments, thesolids component may be treated in an effort to remove lignin and othernon-fermentable components in the C6 stream (or to remove componentssuch as residual acid or acids that may be inhibitory to efficientfermentation) in addition to hydrolyzing (such as enzyme hydrolysis) thesolids component to access the C6 sugars in the cellulose.

Optionally, enzyme hydrolysis efficiency may be increased through theaddition of an agent. Such agents may include anaerobic membranedigester effluent, clarified thin stillage, wet cake, whole stillage,other viable protein source, or combinations thereof.

Optionally, the hexose sugars generated at enzyme hydrolysis system 308may also be treated in a manner similar to pentose treatment system 306via a hexose treatment system (not shown). The removed components duringtreatment and production of ethanol from the biomass from either or boththe C5 stream and the C6 stream (or at distillation) can be treated orprocessed into bioproducts or into fuel (such as lignin for a solid fuelboiler or methane produced by treatment of residual/removed matter suchas acids and lignin in an anaerobic digester) or recovered for use orreuse.

In accordance with the embodiment shown in FIG. 3B, the resultingtreated pentose liquor from treatment system 306 and the hexose sugarfrom enzyme hydrolysis system 308 can be combined for co-fermentation ina fermentation system 318 to generate a fermentation that includes analcohol (e.g., ethanol) and optionally one or more impurities such asdiacetyl. Typically, a fermenting organism (ethanologen) is used in thefermentation system 318. The selection of an ethanologen may be based onvarious considerations, such as the predominant types of sugars suppliedto fermentation system 318.

As shown in FIG. 3B, the fermentation product from the fermentationsystem 318 is supplied to a distillation system 320 where the alcoholsuch as ethanol is recovered. Dehydration and/or denaturing of theethanol produced from the C5 stream and the C6 stream may be performedeither separately or in combination. As described with respect to FIG.3A, the ethanol from distillation system 320 can be processed by atreatment system 330 according to the present invention for theremediation of one or more undesired components (e.g., diacetyl).

Also, any stillage from the distillation system 320 may then be treatedat a lignin separation system (not shown) to generate a liquid componentand a solid wet cake. The wet cake may then be supplied to an AnaerobicMembrane Bioreactor (AnMBR) for further treatment, in some embodiments.

In accordance with the embodiment shown in FIG. 3C, the treated pentoseliquor from treatment system 306 may be fermented in a pentosefermentation system 322, and the fermentation product from fermentationsystem 322 may be supplied to a pentose distillation system 324 forethanol recovery. Likewise, the pretreated solids from separation system304 may be supplied to enzyme hydrolysis system 308 to generate hexosesugars. The hexose sugars can be provided to a hexose fermentationsystem 326 to generate a fermentation product. The fermentation productfrom system 326 can be supplied to a hexose distillation system 328 forethanol recovery.

The ethanol from the pentose distillation system 324 and the hexosedistillation system 328 can be processed by a treatment system 330according to the present invention for the remediation of one or moreundesired components (e.g., diacetyl).

Also, any stillage from the distillation system 324 and/or distillationsystem 328 may then be treated at a lignin separation system (not shown)to generate a liquid component and a solid wet cake. The wet cake maythen be supplied to an Anaerobic Membrane Bioreactor (AnMBR) for furthertreatment, in some embodiments.

The present invention relates to systems and methods to reduce theconcentration of one or more undesirable components (also referred toherein as “remediation” of one or more undesirable components) that aregenerated during at least one of pretreating, saccharification, orfermentation of cellulosic biomass material, or distillation offermented cellulosic biomass material.

In some embodiments, the undesired component includes diacetyl(2,3-butanedione). This is due at least in part to the impact thatdiacetyl can have on the color and/or pH of the quality of the finalethanol fuel product generated in a cellulosic ethanol plant. It isconsidered within the scope of this disclosure that additionalundesirable components may also be remediated through the systems andmethods disclosed herein. As such, no undue limitations should be placedupon components being remediated.

Accordingly, in some embodiments, a method according to the presentinvention includes reducing the concentration of diacetyl that ispresent in a pretreated cellulosic material and/or distillate bycontacting the pretreated cellulosic material and/or distillate with atleast one treatment compound so that the at least one treatment compoundreacts with the diacetyl to form a reaction product thereby reducing theconcentration of the diacetyl.

The reaction of the diacetyl with the treatment compound can convert thediacetyl (boiling point 88° C.) into a relatively less volatile reactionproduct such that a mixture of the ethanol and the reaction product canbe subjected to a separation process that takes advantage of the lowerboiling point of the reaction product thereby facilitating thepurification of the ethanol with respect to the impurity diacetyl (orthe reaction product thereof).

One or more treatment compounds can be selected so as to react with animpurity such as diacetyl and form a reaction product so as to reducethe concentration of the diacetyl. Preferably, the one or more treatmentcompounds are selected so that the reaction product is readily separatedfrom the pretreated cellulosic material and/or distillate (andultimately the alcohol such as ethanol). In some embodiments, thetreatment compounds includes an oxidizing agent, an alkali compound, andmixtures thereof. In some embodiments, the oxidizing agent includeshydrogen peroxide. In some embodiments, the alkali compound includessodium hydroxide.

In some embodiments, the concentration of diacetyl is reduced so thatthe color and/or pH are within one or more specifications for sellingethanol as a fuel. For example, preferably the diacetyl concentration isdecreased so that the treated ethanol product from distillation iswithin product color specifications for selling ethanol as a fuel (i.e.,is not green in color to an undue degree). Diacetyl can cause ethanol tobe green to an undue degree at even 20-30 ppm in some instances. In someembodiments according to the present invention, the color of the ethanolafter remediation according to the present invention is clear andbright. Typically, the ethanol is separated from the reaction productvia, e.g., a re-vaporization process before the ethanol comes withinfinal color specifications. For example, when sodium hydroxide is addedto a ethanol/diacetyl mixture the color changes from a yellow-green(color of ethanol/diacetyl mixture) to a dark yellow-orange due to thereaction between sodium hydroxide and diacetyl.

With respect to pH, diacetyl can cause ethanol to be out ofspecification for sale as fuel because diacetyl can degrade into acid.The stoichiometric degradation of 1.0 ppm diacetyl yields 1.4 ppm aceticacid. Remediation of diacetyl according to the present inventionpreferably causes an increase in pH of the ethanol product to be sold asfuel so that the ethanol product is within one or more specificationsfor the sale of the ethanol product as fuel. For example, preferably thepretreated cellulosic material and/or distillate is contacted with anamount of an alkali compound (e.g., sodium hydroxide) so that the pH ofthe pretreated cellulosic material and/or distillate is at least 10,even more preferably at least 12.

In terms of the concentration level of diacetyl, the concentration ofdiacetyl in the final ethanol product (e.g., after re-vaporizationdiscussed below) is preferably in an amount of 100 parts per million orless, 50 parts per million or less, 20 parts per million or less, orpreferably even 10 parts per million or less.

At least one advantage of the remediation techniques of the presentinvention is the relative decrease in time period required to remediatea given amount of diacetyl as compared to “aging” a mixture for thediacetyl to break down. In some embodiments, wherein the concentrationof diacetyl in the distillate can be reduced from at least 50, at least100, or even at least 200 parts per million to 40, 20, 10, or even 5parts per million or less in a time period of 60, 30, 20, or even 10minutes or less.

Optionally, a method of remediation according to the present inventioncan include exposing pretreated cellulosic material and/or distillate toultraviolet radiation to degrade one or more impurities and therebyreduce the concentration thereof of such impurities. The material to beremediated can be exposed to ultraviolet light at any time such asbefore, during, and/or after contacting the material with at least onetreatment compound as described herein.

After the at least one treatment compound reacts with the diacetyl toform a reaction product, at least a portion of the reaction productand/or at least a portion of any residual diacetyl can be separated fromthe ethanol so as to increase the concentration of the ethanol.Preferably, after separating at least a portion of the reaction productand/or at least a portion of any residual diacetyl from the ethanol, theethanol satisfies one or more specifications with respect to at leastdiacetyl and/or pH for selling ethanol as fuel.

The reaction product and/or any residual diacetyl can be separated fromthe alcohol by any technique. An exemplary separation technique includesvaporizing (also referred to as “re-vaporizing” in the context ofoccurring after distillation of a fermentation product) a mixture (e.g.,a distillate) including at least alcohol, the reaction product ofdiacetyl and at least one treatment compound, and any residual diacetyl.Vaporizing is preferably performed under conditions to form a liquidfraction and a vapor fraction, where the vapor fraction includes atleast a portion of the alcohol and the concentration of the alcohol inthe vapor fraction is higher as compared to the concentration of thealcohol in the initial mixture (e.g., the distillate). In someembodiments, the vapor fraction from the vaporization process includesat least 100 proof ethanol, preferably at least 120 proof ethanol, andeven preferably at least 150 proof ethanol.

Also, the liquid fraction from the vaporization process preferablyincludes at least a portion of the reaction product and theconcentration of the reaction product in the liquid fraction is higheras compared to the concentration of the reaction product in the initialmixture (e.g., the distillate).

FIG. 4 illustrates an exemplary system for reducing the concentration ofdiacetyl that is present in a pretreated cellulosic material. Theindividual equipment/components described in connection with FIG. 4 arewell-known and commercially available. As shown, a rectifier 402 isillustrated that delivers a mixture 190 proof ethanol vapor andrelatively high levels of the diacetyl to condenser 404 where themixture is condensed. The resulting condensed ethanol solution iscollected in a rundown tank 406. Optionally, a portion of the ethanolcollected in the rundown tank can be returned to the rectifier 402 as areflux (not shown). The remaining ethanol/diacetyl solution is mixedwith a treatment compound prior to being supplied to a vaporizer 410. Atreatment pump 408 drives the treatment compound and ensures accuratedosing. In the vaporizer 410 the mixed liquid is heated. The resultingvapor is supplied to a superheater 412 which results in a 190 proofethanol vapor stream that has virtually all the undesirable compounds(e.g., diacetyl) removed. A purge stream from the vaporizer 410 issupplied back to the rectifier 402.

EXAMPLES Example 1

The first example proceeded using a 7% H₂O₂ solution that was used fordiacetyl mitigation during a batch distillation run. A known volume ofcellulosic ethanol was heated to 60° C. then treated with 10% by volumeof a 7% H₂O₂ solution. The ethanol was kept at 60° C. with constantstirring after the treatment and samples were taken for HPLC analysisfollowing the treatment at 0 hour, 1 hour and 2 hour; then the samplewas distilled. The results show a 63% reduction in diacetyl immediatelyfollowing the treatment with a 91% reduction at one hour post treatment.The HPLC results are shown below in Table 1

TABLE 1 Reduction H₂0₂ Mitigation - Acetic of 10% H₂O₂ Acid EthanolDiacetyl Diacetyl (7% H₂O₂) ppm % v/v ppm Color % 100 proof  27 56 123 slight green Mitigation-0 hr @60 C. 299 53 45 clear 64 Mitigation-1 hr@60 C. 203 53 12 clear 91 Mitigation-2 hr @60 C. 168 53 ND clear 100Distillate ND 100 ND clear 100 Still Bottoms 181 47 ND clear 100

Example 2

The second example proceeded using a 1.0N solution of sodium hydroxide(NaOH). A known volume of cellulosic ethanol was heated to 60° C.,treated with 0.2% by volume of a 1.0N NaOH solution, and then distilled.Duplicate test results are shown in Table 2 below. The distillate andthe still bottoms are within industry specifications.

TABLE 2 NaOH Mitigation-0.2% NaOh (1.0N) Acetic Di- Sample Acid Ethanolacetyl Description ppm % v/v ppm Color pH pHe Feed-100 proof 34 50 102slight green 4.3 0.2% NaOh 60 50 ND clear 11.4 (1.0N) Distillate ND 101 33 clear 7.3 Still Bottoms 107  29 ND orange-brown 7.5 Feed-100 proof25 52 100 slight green 4.4 0.2% NaOH 53 52 ND clear 11.5 (1.ON)Distillate ND 95  33 clear 8.3 Still Bottoms 119  30 ND orange-brown 8.1

Example 3

A mitigation strategy to treat the cellulosic ethanol with a combinationof H₂O₂ and NaOH was devised. Based on previous results for hydrogenperoxide and sodium hydroxide mitigation, several tests were conductedto determine the optimum dosage of both. Table 3 shows the results for amitigation treatment of 1% by volume of a 7% H₂O₂ solution followed by0.01% by volume of a 50% w/w NaOH solution. The results show thatdiacetyl is converted to acetic acid and the distillate color is clear.

TABLE 3 H₂O₂ + NaOH Mitigation - 1% H₂O₂ (7%) + 0.01% NaOH (50%) AceticEtha- Sample Mass Acid nol Diacetyl Description (g) ppm % v/v ppm ColorpH Feed-100 proof  44 51 83 slight green 4.45 1% H₂O₂ (7%) + 462.7 19551 ND clear 6.8 0.01% NaOH (50%) Distillate 134.9 ND 101 ND clear 9.45Still Bottoms 321.2 237 26 ND clear 5.08

Several batch distillations were completed to determine alternatetreatments that remove the diacetyl but maintains the ethanol in a moredesirable pHe. The test results are displayed in Table 4 for themitigation treatment of 2% by volume of a 7% H₂O₂ solution followed by0.2% by volume of a 1.0N NaOH solution. The distillate was clear incolor, the HPLC results confirm there was no diacetyl and the pH islower.

TABLE 4 H₂O₂ + NaOH Mitigation - 2.0% H₂O₂ (7% H₂O₂) + 0.2% NaOH (1.0N)in 200 Bell ethanol diluted to 100 proof Ace- Distillations tic Di- MassAcid Ethanol acetyl Fraction # (g) ppm % v/v ppm Color pH pHe Feed-  2551 100  slight green 4.42 100 proof 2% H₂O₂  68 50 59 slight green 4.23(7%) 0.2% NaOH 462.5 143 50 ND clear 6.52 (1.0N) Distillate 139.1 ND 99ND clear 7.64 Still 319.1 257 25 BDL clear 4.88 Bottoms Feed-  32 51102  slight green 4.43 100 proof 2% H₂O₂ 131 50 35 slight green 4.23(7%) 0.2% NaOH 463.0 149 50 ND clear 6.54 (1.0N) Distillate 131.5 ND 99ND clear 8.06 Still 324.1 228 26 BDL clear 5.02 Bottoms Feed-  23 51 97slight green 4.41 100 proof 2% H₂O₂  88 50 54 slight green 4.26 (7%)0.2% NaOH 470.6 146 50 ND clear 6.53 (1.0N) Distillate 129.3 ND 101 NDclear 7.10 Still 323.4 246 25 ND clear 4.84 Bottoms

Example 4

An example was performed at elevated temperature. A sample of cellulosic100 proof ethanol was subjected to the mitigation treatments of 10% and5% by volume of a 7% H₂O₂ solution, 0.1% by volume of a 50% w/w NaOHsolution, 0.2% by volume of a 1N NaOH solution, and 2% by volume of a 7%H₂O₂ solution followed by 0.2% by volume of a 1N NaOH solution. Thesamples were placed into a 60° C. water bath immediately after beingdosed with the treatment at time zero. Samples were removed from theheated water bath and placed into an ice bath at set time points, andthen analyzed by HPLC. Samples that were treated with stronger doses ofsodium hydroxide turned yellow-orange immediately after addition, anddarkened to a pink color after time at the elevated temperature. Whenleft at room temperature overnight, all samples had changed to the samepink color. Lower doses of sodium hydroxide resulted in less color, andthe combination treatment of hydrogen peroxide and sodium hydroxideshowed no color change.

FIGS. 5-7 illustrate the results of this example study. In FIG. 5, thesamples treated with H₂O₂ are illustrated as the diacetyl concentrationover time (at 500). Diacetyl levels decrease over time and reaches verylow levels at approximately 60 minutes. In FIG. 6, the samples treatedwith NaOH are illustrated as the diacetyl concentration over time (at600). Here the diacetyl decreases almost instantaneously after causticapplication. A similar response is seen in FIG. 7, where samples treatedwith NaOH and H₂O₂ are illustrated (at 700).

Example 5

A further example for mitigation treatments illustrates that thatexposure to light also reduces diacetyl in cellulosic ethanol. Samplesof 200 proof cellulosic ethanol were tested under three differentconditions. The first was placed in a capped glass jar that was placedin the hood under light 24/7, the second was treated with 0.1% by volumeof a 7% H₂O₂ solution (one dose at time zero only) and stored in thehood under light 24/7, and the third was treated with 0.1% by volume ofa 7% H₂O₂ solution then placed in the dark. Aliquots of each sample weretaken periodically and analyzed on the HPLC. FIG. 8 shows the trend forthe diacetyl reduction in these three conditions. The samples treatedwith peroxide showed an initial reduction more pronounced than thesample not treated with peroxide, however light also affect the speed ofdiacetyl reduction. The sample stored in the dark showed the slowestreduction over time.

Example 6

The diacetyl mitigation process was also demonstrated in a larger pilotplant. FIG. 9 describes the diacetyl concentration in the 190 proofsamples collected after distilling five fermentation batches. Theconcentration of diacetyl in the distilled 190 proof ranged from 60 ppmto 126 ppm and averaged 90 ppm. Among other final product specificationsaffected by the presence and composition of diacetyl, color is the mostprominent. The visible color threshold in this example is shown to bearound 20-30 ppm diacetyl.

Grab samples were collected for each of five fermentation batchesthrough distillation, as well as two composite samples. The ethanolconcentration of the five fermentation batches averaged 89.96% (180proof), while composite samples at 24 hours and 48 hours averaged83.57%. The difference in ethanol concentration is presumably fromstartup and shutdown procedures for distillation that allow more waterto stay in vapor form. The pHe of the ethanol samples decreased asacetic acid concentration increased over time in storage as a result ofdiacetyl degradation. The acetic acid formed from diacetyl significantlyincreases the amount of NaOH required for mitigation.

FIG. 10 describes the effect of NaOH on the pHe of the batch grabsamples of 190 proof ethanol. FIG. 11 shows the NaOH and pHerelationship for the 24 and 48-hour composite samples, overlaid with thegrab samples. From the data presented in FIG. 10, a significant increasein pHe was observed between 0.08 g/L and 0.12 g/L NaOH for individualgrab samples. However, FIG. 11 shows the NaOH dose required to reachtarget pHe is increased to 0.22 g/L NaOH in the composite 190 proofsamples due to the presence of acetic acid.

FIG. 12 details the effect of pHe on diacetyl concentration for the graband 24-hour composite 190 proof samples. From this figure, a pHe greaterthan 12.5, in general, reduced diacetyl concentrations to less than 10ppm, with complete diacetyl destruction occurring after the pHe reached13.0 for all samples analyzed.

The 190 proof grab samples required between 0.10 and 0.14 g/L NaOH toachieve a diacetyl concentration below detectable limits. However, the24 and 48-hour composite samples required 0.22 and 0.27 g/L NaOH,respectively, to reach 13.0 pHe for complete diacetyl mitigation. Usingthe 48-hour composite titration result from FIG. 11, including anadditional 20% safety factor, the dosing requirement to reach 13.0 pHefor pilot scale mitigation was determined to be 0.35 g/L NaOH.

FIG. 13 compares the composite 190 proof ethanol samples. The 24-hourcomposite sample was processed on the HPLC immediately following NaOHtitration. The resulting pHe vs. diacetyl curve closely matches the grabsamples in that there was a definitive break in pHe value before areduction in diacetyl concentration was observed. The 48-hour pHe vs.diacetyl curve was affected by increased reaction time between titrationwith NaOH and HPLC analysis.

The principle difference between the composite and grab samples was thepresence of acetic acid. No acetic acid was detected in the grabsamples, while the 24 and 48-hour composite samples contained 27 ppm and52 ppm acetic acid, respectively. The samples of 190 proof starchethanol containing 0 and 27.9 ppm acetic acid were titrated and theresults are presented in FIG. 14 which shows the dosage of NaOH requiredto adjust the samples to a pHe of 13.0. The sample containing no aceticacid required only 0.06 g/L NaOH to reach the desired pHe of 13.0.However, the sample containing 30 ppm acetic acid significantlyincreased the buffering capacity of the ethanol, requiring nearly 0.13g/L NaOH.

This acetic acid buffering effect directly influences the amount of NaOHrequired for dosing. If the acetic acid concentration present in the 190proof cellulosic ethanol can be held to a minimum, the NaOH doserequired for ethanol is reduced from 0.35 g/L to 0.14 g/L NaOH(including the 20% safety factor).

Lastly, in order to more accurately reflect commercial scale remedialsystems, an example is provided where a forced circulation evaporatorwas used to vaporize pH adjusted cellulosic 190 proof ethanol atatmospheric pressure. A steady flow of 190 proof ethanol was supplied at0.9-0.75 gpm to the separator of the evaporator. A peristaltic pump wasused to supply 1N NaOH to the vaporizer feed line at a targeted 0.35 g/LNaOH. Steam pressure was controlled to produce a steady distillate flow.A purge, or recycle, stream was operated to maintain a steady level inthe separator. The distillate stream and the concentrate purge streamwere collected separately for analysis.

FIG. 15 shows the diacetyl concentration in the untreated 190 proof wasreduced from 80 ppm to <10 ppm with an average value of 6.4 ppm. HPLCanalysis was also performed on both the feed and concentrate streams.

Acetic acid present in the composite 190 proof ethanol sampleaccumulated in the vaporizer and had not reached equilibrium with purgevolume by the end of the experiment. FIG. 16 shows the acetic acidpresent in the feed and its accumulation in the vaporizer.

What is claimed is:
 1. A system for reducing the concentration ofdiacetyl that is present in a pretreated cellulosic material comprising:a source of a fermentation product comprising: an alcohol; and diacetyl;a distillation system in fluid communication with the source of afermentation product, wherein the distillation system can distill thefermentation product to form a distillate comprising the alcohol and thediacetyl; a source of at least one treatment compound, wherein the atleast one treatment compound is chosen from an oxidizing agent, analkali compound, and mixtures thereof; and a treatment system in fluidcommunication with the distillation system and the source of at leastone treatment compound, wherein the treatment system causes the leastone treatment compound to contact the distillate so that the at leastone treatment compound reacts with the diacetyl to form a reactionproduct thereby reducing the concentration of the diacetyl and forming atreated distillate.
 2. The system of claim 1, further comprising avaporizing system in fluid communication with the treatment system,wherein the vaporizing system can subject the treated distillate to avaporization process to vaporize at least a portion of the treateddistillate to form a liquid fraction and a vapor fraction, wherein thevapor fraction comprises at least a portion of the alcohol and theconcentration of the alcohol in the vapor fraction is higher as comparedto the concentration of the alcohol in the treated distillate.
 3. Thesystem of claim 2 wherein the liquid fraction from the vaporizationprocess comprises at least a portion of the reaction product and theconcentration of the reaction product in the liquid fraction is higheras compared to the concentration of the reaction product in the treateddistillate.
 4. The system of claim 1, wherein the treatment systemfurther comprises an ultraviolet light system that can expose thedistillate to ultraviolet light to reduce the concentration of thediacetyl.
 5. The system of claim 1, wherein the at least one treatmentcompound is chosen from an hydrogen peroxide, sodium hydroxide, andmixtures thereof.
 6. A method of reducing the concentration of at leastone impurity that is present in a distilled alcohol comprising:providing a feedstock; subjecting the feedstock to a fermentationprocess to form a fermentation product comprising: an alcohol; and animpurity; distilling the fermentation product to form a liquiddistillate comprising the alcohol and the impurity, the impurity beingpresent in the liquid distillate in a first concentration; andcontacting the liquid distillate with at least one treatment compound sothat the at least one treatment compound reacts with the impurity toform a reaction product thereby forming a treated liquid distillate, thereaction product having a higher boiling point than the alcohol, whereinthe at least one treatment compound is chosen from an oxidizing agent,an alkali compound, and mixtures thereof; and subjecting the treatedliquid distillate to a vaporization process to form a liquid fractionand a vapor fraction, wherein the vapor fraction comprises at least aportion of the alcohol, the vapor fraction containing a concentration ofthe impurity that is lower than the first concentration.
 7. The methodof claim 6, wherein the at least one treatment compound compriseshydrogen peroxide.
 8. The method of claim 6, wherein the impuritycomprises diacetyl.
 9. The method of claim 6, wherein the reactionproduct comprises acetic acid.
 10. The method of claim 6, wherein thealcohol comprises ethanol.
 11. The method of claim 6, wherein the vaporfraction is at least 150 proof ethanol.
 12. The method of claim 11,wherein the vapor fraction is condensed to a post treatment liquid thatis at least 150 proof ethanol, the post treatment liquid having aconcentration of the impurity that is lower than the firstconcentration.
 13. The method of claim 6, wherein the at least onetreatment compound comprises sodium hydroxide.
 14. The method of claim13, wherein the distillate is contacted with an amount of sodiumhydroxide so that the pH of the distillate is at least
 10. 15. Themethod of claim 13, wherein the distillate is contacted with an amountof sodium hydroxide so that the pH of the distillate is at least
 12. 16.The method of claim 6, wherein the distillate comprises alcohol, whereinthe impurity is present in the distillate at a concentration of at least50 parts per million, and the distillate is contacted with the at leastone treatment compound so that the concentration of the impurity isreduced to 20 parts per million or less in a time period of twentyminutes or less.
 17. The method of claim 6, further comprising exposingthe distillate to ultraviolet light to reduce the concentration of theimpurity.
 18. The method of claim 17, wherein the exposing thedistillate to ultraviolet light can occur before, during, or aftercontacting the distillate with at least one treatment compound.
 19. Themethod of claim 6, wherein the providing a feedstock comprises providingcellulosic material.
 20. The method of claim 19, wherein the cellulosicmaterial comprises at least corn stover.